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Order II. MOLLUSCA. ACEPHALA, 



Section I. BRACHIOPODA. 



Shell with two valves ; lobes of the cloak free anteriorly ; arms is- 

 suing from between the lobes at the margin of the mouth ; all the 

 species are marine and permanently attached. 



Pedunculata. 



a. Shell supported on a fleshy peduncle. 

 Lingula. 



I. Peduncle passing through the apex of one valve. 

 Terebratula. 



Spirifer. 

 Mayas. 



Sesselia. 

 Discina. 

 Criopus. 



Obscure genera, apparently free, and extinct. 

 Pentamerus. 

 Productus. 



